On prothetic continua (apparent length, duration, area, etc.) the ratio scale of subjective magnitude approximates a power function of the physical stimulus. The category scale is concave downward relative to the ratio scale for discrimination which is better at one end of the continuum than at the other. On metathetic continua (visual position, inclination, pitch, etc.) discrimination (in subjective units) is constant over the range, although differential familiarity may introduce nonuniformities. Additional aspects of the continua and scales are discussed. 75 references. (PsycINFO Database Record (c) 2006 APA, all rights reserved)